#include<stdio.h>

#define MAX(a,b) ((a)>(b)?(a):(b))

int main(void){

	int N;
	scanf("%d",&N);

	int *V;
	V=(int *)malloc(sizeof(int)*N);
	int i;
	for(i=0;i<N;i++) scanf("%d",&V[i]);

	if(N==1){
		printf("%d\n",V[0]);
		return 0;
	}

	int a=V[N-1];
	int b=V[N-2]>a?V[N-2]:a;

	while(N>2){
		int c=MAX(b,a+V[N-3]);
		a=b;
		b=c;
		N--;
	}
	printf("%d\n",b);
	return 0;
}